This invention relates to a display system with a linear array of electromechanical grating devices that is scanned in order to generate a two-dimensional image. More particularly, the invention relates to a high-contrast laser display system containing electromechanical conformal grating devices.
Spatial light modulators based on electromechanical grating devices are important for a wide range of applications, including display, data storage, spectroscopy and printing. Such systems require large numbers of individually addressable devices in either a linear or area array, with over a million addressable devices desirable for an area modulator array in a high-quality display.
Recently, an electromechanical conformal grating device consisting of ribbon elements suspended above a substrate by a periodic sequence of intermediate supports was disclosed by Kowarz in U.S. Pat. No. 6,307,663, entitled xe2x80x9cSpatial Light Modulator With Conformal Grating Devicexe2x80x9d issued Oct. 23, 2001. The electromechanical conformal grating device is operated by electrostatic actuation, which causes the ribbon elements to conform around the support substructure, thereby producing a grating. The device of ""663 has more recently become known as the conformal GEMS device, with GEMS standing for grating electromechanical system. The conformal GEMS device possesses a number of attractive features. It provides high-speed digital light modulation with high contrast and good efficiency. In addition, in a linear array of conformal GEMS devices, the active region is relatively large and the grating period is oriented perpendicular to the array direction. This orientation of the grating period causes diffracted light beams to separate in close proximity to the linear array and to remain spatially separated throughout most of an optical system.
While ideal conformal GEMS devices have perfectly planar ribbon elements, fabrication, processing, and material selection can result in actual ribbon elements having an appreciable curvature. Since the ribbon elements are periodic, the ribbon curvature is also a periodic sequence. In a display system, this periodic ribbon curvature produces unintended diffracted light beams that can potentially reduce image contrast if allowed to pass through the optical system and reach the display screen. These unintended beams, referred to as diffracted cross-orders, reduce contrast because they are present even when the conformal GEMS device is in the non-actuated state. There is a need, therefore, for a high-contrast display system, based on conformal GEMS devices, that does not allow diffracted cross-orders to pass through the optical system.
The need is met according to the present invention by providing an improved projection system that includes a conformal grating electromechanical system (GEMS) device for forming an image on a medium, and also including: a light source providing illumination; a linear array of conformal GEMS devices receiving the illumination; an obstructing element for blocking a zeroth order reflected light beam from reaching the medium; a cross-order filter placed substantially near a Fourier plane of a lens system for blocking a plurality of diffracted cross-order light beams from reaching the medium; a scanning element for moving non-obstructed diffracted light beams relative to the medium; and a controller for providing a data stream to the individually operable devices.